1. Field of the Invention
The present invention relates to a fiber laser beam processing apparatus that executes laser beam processing using a fiber laser beam.
2. Description of the Related Art
Recently, a fiber laser beam processing apparatus has been practically used that executes desired laser beam processing by applying a laser beam generated by a fiber laser onto a work to be processed.
A conventional fiber laser beam processing apparatus uses as an optical fiber for oscillation a double-clad fiber (DCF) having a two-layer clad structure including an inner clad and an outer clad; causes an excitation beam to propagate in the axial direction confining the beam in the inner clad by the total reflection on the interface between the clads; causes the beam to cross a core many times during the propagation; thereby, causes an excitation element in the core to be pumped; and takes out an oscillated beam or a fiber laser beam having a predetermined wavelength from an end face of the core in the axial direction. The apparatus uses a laser diode (LD) as an excitation light source and is adapted to condense and inject an excitation laser beam of the LD onto the end face of the DCF through an optical lens.
In addition to the above DCF laser of an LD end-face excitation scheme, the conventional fiber laser beam processing apparatus also uses a fiber laser of a so-called “pigtail scheme” having a configuration according to which multiple optical guides (for example, optical fibers) are branched in the form of branches from the side of an oscillating optical fiber and an LD for excitation is integrally coupled to the tip of each of the guides.
As above, a laser beam of an LD that is small and light and has a high luminous efficiency is used as the excitation beam of the fiber laser. However, an LD beam has a poor beam quality concerning the beam mode and convergence thereof. Therefore, a DCF laser of the LD end-face excitation scheme in the conventional fiber laser beam processing apparatus has a low optical coupling efficiency between the excitation LD and the DCF and, as a result, obtaining a high output fiber laser beam is difficult using the DCF laser. According to the pigtail scheme, a laser beam from an LD for excitation is supplied to an optical fiber for oscillation through an optical fiber (a branched fiber). Therefore, the coupling efficiency or the excitation efficiency thereof is high and a high output fiber laser beam can be obtained relatively easily. On the contrary, an excitation unit (the optical guide and the LD for excitation) is complicated and bulky. In addition, because the unit is physically integrally coupled to the optical fiber for oscillation, a problem has arisen that maintenance and repairing of components therein (especially the LD for excitation) is difficult.